HIV has been one of the worst killers of the past few decades worldwide — but now it may yield a cure for cancer. Scientists in Korea have been using the virus to cure lung cancer (in mice, at least.)

South Korean scientist Myung-Haing Cho modified a lentivirus, a genus in the Retroviridae family which includes most mammal immunodeficiency viruses, to deliver to lung-cancer tumors a gene, which inhibits cancer cells from reproducing in mice's lungs. Their method of choice? A nasal spray.

They had various cancer-ridden mice sniff the modified lentivirus twice a week for a month, and they found that the modified virus completely halted the progression of the lung cancer without harm to the non-cancerous tissue. In some cases, existing cancer cells even died off without further therapy.

Scientists consider modified lentiviruses ideal for cancer therapy (in addition to other gene therapies) because it affects even non-replicating cells (like neurons) and can create long term changes, positive changes in genes.

Of course, anybody who's seen I Am Legend knows that the "genetically engineered virus that fights cancer" thing can only end one way.